This application is based on and claims priority under 35 U.S.C. xc2xa7 119 with respect to Japanese Application No. 2000-054235 filed on Feb. 29, 2000, the entire content of which is incorporated herein by reference.
The present invention generally relates to a support bar and method of forming a support bar. More particularly, the present invention pertains to a support bar used in a headrest assembly for supporting the headrest in its adjusted position, or used in a hand brake for maintaining an operated position of the hand brake by engaging the support bar with a hand brake ratchet, as well as a method for forming such a support bar.
A known type of support bar and method for forming such a support bar is disclosed in Japanese Patent Application Publication published as Toku-Kai-Hei 8(1996)-90125. FIG. 7 illustrates the method disclosed in this publication for forming a dent or notch on the outer peripheral portion of a hollow pipe member that serves as an engagement mechanism allowing the pipe member to serve as a support bar. In the disclosed method, the hollow pipe is fixed by a die device having lower and upper die parts. A punch 92 movable through the upper die part presses against the outer periphery of the pipe member in the radial direction of the pipe member to form the dent or notch. To take into account possible variations in the outer diameter of the pipe, the inner diameter of the die parts of the die device must be slightly larger than the outer diameter of the pipe to prevent the pipe member from being clinched or seized in the die parts.
However, because of this difference in diameter, it occasionally happens that the pipe member cannot be properly fixed by the die parts of the die device. When the pipe member is not firmly fixed by the die device and the forming surface on the top of the punch is concave, the unstable nature of the pipe member during the notch forming process results in the formation of unwanted additional material portions 91 (burr-like projections) that extend or expand outwardly beyond the generally smoothly curved outer periphery of the pipe member and at the side end parts of the notch or indented portion as shown in FIGS. 8 and 9. These additional material portions 91 may also be generated when the surface of the punch is flat as shown in FIG. 9.
In the case of, for example, a headrest assembly, because the support bar is slidably supported through a guide member that is attached on the vehicle seat, these additional material portions may interfere with the smooth sliding movement of the support bar in the guide member. As a result, it is necessary to implement additional processing steps to remove these additional material portions 91 and this undesirably increases the manufacturing costs.
In light of the foregoing, a need exists for a support bar and method of manufacturing a support bar that is not as susceptible to the formation of additional material portions extending outwardly beyond the smoothly curved outer periphery of the support bar.
According to one aspect of the invention, a support bar includes an elongated pipe member provided with at least indented portion formed on the outer peripheral surface of the pipe member by press stamping. The indented portion has a bottom surface portion possessing a continuous concave curvature as seen in a cross-section perpendicular to the longitudinal axis of the pipe member.
According to another aspect of the invention, a support bar includes an elongated pipe member provided with at least press-stamped indented portion on the outer peripheral surface of the pipe member. The indented surface portion has an inclined surface portion that is inclined relative to the longitudinal axis of the pipe member. The inclined surface portion possesses a concave curvature as seen in a cross-section perpendicular to the longitudinal axis of the pipe member.
Another aspect of the present invention involves a method for making a support bar. The method includes fixing a pipe member in a die device having at least three die parts so that the pipe member is positioned parallel to the die parts and with the die device encircling a portion of the outer peripheral surface of the pipe member. A punch is inserted into a through hole formed in the die device and towards the outer peripheral surface of the pipe member. The punch has a convexly shaped free end surface facing the outer peripheral surface of the pipe member as the punch is inserted into the through hole. The free end surface of the punch is pressed against the outer peripheral surface of the pipe member to form an indented portion on the outer peripheral surface of the pipe member.